Engineered neck angle ammunition casing

ABSTRACT

Polymeric ammunition casings having engineered neck geometries, and methods of forming such ammunition are provided. In particular embodiments, both the internal and external neck geometries are engineered to provide even greater improvement of the accuracy and consistency of the ammunition.

CROSS-REFERENCE TO RELATED APPLICATIONS

The current application is a divisional application of U.S. patent application Ser. No. 14/448,905 filed Jul. 31, 2014, which application claimed priority to U.S. Provisional Application No. 61/860,831, filed Jul. 31, 2013, the disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The current application relates to ammunition casing, and more particularly to ammunition casing having an engineered neck angle.

BACKGROUND OF THE INVENTION

Accuracy of an ammunition cartridge is an important quality that is the cumulative result of many individual variable contributions such as: cartridge geometry, materials of construction and loading configuration. For the high accuracy shooter, many of these variable contributions are circumvented by ensuring round to round consistency. There are, however, some inherent qualities, such as geometry, that lead to superior accuracy performance. Cartridges that take full advantage of these design criteria to improve accuracy and round consistency would be of great technological advantage.

SUMMARY OF INVENTION

In many embodiments the invention is directed to an ammunition article comprising at least a casing having a neck region in which the interior and exterior walls are independently configurable.

In some embodiments the ammunition article includes:

-   -   a casing defining a generally cylindrical hollow body having         internal and external walls, the casing having a cap at a first         end thereof and a pressure vessel at a second end thereof, the         pressure vessel having a proximal end defining a body region and         a distal end defining a neck region, wherein the cap is         interconnected with the proximal end of said pressure vessel         such that the casing at least partially encloses an internal         volume, and wherein the diameter of the pressure vessel narrows         from a first diameter at the body region to a second diameter at         the neck region;     -   wherein at least the neck region of the pressure vessel at least         partially comprises a substantially polymeric material; and     -   wherein the geometry of the internal and external walls of the         casing in the neck region of the casing are independent of each         other.

In other embodiments the casing in the neck region defines an internal wall that is linear and non-parallel with the external wall of the casing in the neck region. In some such embodiments the external and internal walls in the neck region have define an external and internal angle relative to a longitudinal axis of the casing, wherein the angular ratio of the external angle to the internal angle is a non-unity value. In other such embodiments, the angular ratio is less than about 0.95. In still other such embodiments the angular ratio is greater than about 1.10.

In still other embodiments the casing in the neck region defines an internal wall that forms a generally circular arc relative to a linear external wall. In some such embodiments the arc of the internal wall of the neck region defines a ratio of the radius of the arc to the length of the neck region of the casing of between about 0.1 and 50.

In yet other embodiments the casing in the neck region defines an internal wall that forms a generally elliptical arc relative to a linear external wall. In some such embodiments the elliptical arc of the internal wall of the neck region is defined by an ellipse value determined by the sum of the distances from any two points within a plane of the ellipse to any single point on the circumference of the ellipse, and wherein the ellipse value ranges from about 0 to 10 inches.

In still yet other embodiments the internal wall of the neck region is defined by a plurality of regions selected from the group of non-colinear consecutive lines, more than one arc in a spline curve, a combination of non-parallel lines, and a combination thereof. In some such embodiments, the plurality of regions are blended together using chamfers or fillets.

In still yet other embodiments the interior wall of the neck region of the casing has at least one point that is narrower than the inner diameter of the distal end of the pressure vessel in which a projectile would be inserted. In some such embodiments the at least one point in the neck region is disposed such that a projectile inserted into the casing would impinge thereon.

In still yet other embodiments the casing is one-piece.

In still yet other embodiments the polymeric material comprises at least 10% of the casing by weight.

In still yet other embodiments the cap comprises a metal.

In still yet other embodiments the cap and the caselet are joined using an interconnection selected from the group consisting of a snap fit, threads, snap fit in conjunction with an adhesive, and threads in conjunction with an adhesive.

In still yet other embodiments the casing is closed at its distal end and contains no projectile.

In still yet other embodiments the article includes a projectile fitted into the distal end of the casing. In some such embodiments the projectile is secured to the casing by an interconnection selected from the group consisting of molding the polymeric material around the projectile, mechanical interference, an adhesive, ultrasonic welding, the combination of molding in place and adhesive, and hot crimping after molding.

In still yet other embodiments the pressure vessel comprises at least two pieces.

Additional embodiments and features are set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the specification or may be learned by the practice of the disclosed subject matter. A further understanding of the nature and advantages of the present disclosure may be realized by reference to the remaining portions of the specification and the drawings, which forms a part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The description will be more fully understood with reference to the following figures and data graphs, which are presented as various embodiments of the disclosure and should not be construed as a complete recitation of the scope of the disclosure.

FIG. 1 shows an image comparing the 0.338 Lapua Magnum cartridge (left) and the 0.338 Norma Magnum cartridge (right).

FIG. 2 shows an image providing the production steps of brass cartridges.

FIG. 3a is a semi-schematic, perspective view of an ammunition article provided in accordance with embodiments of the present invention.

FIG. 3b is a semi-schematic, exploded view of the ammunition casing components in accordance with embodiments of the present invention.

FIG. 3c is a perspective view of the cartridge casing provided in accordance with embodiments of the present invention in which the first pressure vessel component is comprised of two individual components.

FIG. 3d is a perspective view of the cartridge casing provided in accordance with embodiments of the present invention in which the pressure vessel component is comprised of three individual components.

FIG. 4 is a cross-sectional view of the cartridge casing provided in accordance with embodiments of the present invention in which the pressure vessel component is skeletonized and a lightweight component is overmolded over the pressure vessel skeleton.

FIGS. 5a and 5b provide schematics of external (5 a) and internal (5 b) caselet geometries in accordance with embodiments of the present invention.

FIGS. 6a and 6b provide schematics of convex (6 a) and concave (6 b) caselet geometries in accordance with embodiments of the present invention.

FIG. 7 provides a schematic of a caselet geometry in accordance with embodiments of the present invention.

FIG. 8 provides a schematic showing exemplary ellipse geometries.

FIG. 9 provides a schematic of a caselet geometry incorporating protruding features in accordance with embodiments of the present invention.

FIG. 10 provides a schematic of a caselet geometry in accordance with Example 3 of the current disclosure.

DETAILED DESCRIPTION OF INVENTION

Turning to the drawings and description, embodiments of polymeric ammunition casings having engineered neck geometries, and methods of forming such ammunition are provided. In particular, embodiments, both the internal and external neck geometries are engineered to provide even greater improvement of the accuracy and consistency of the ammunition.

Although there are many parameters that can be adjusted in attempting to improve the accuracy and consistency of ammunition, one specific geometric feature that is of current interest is the angle of the shoulder region that connects the gentle-tapered case body to the straight neck area. It is currently believed that altering the angles (relative to a horizontal axis) may lead to higher accuracy rounds. One such example, as shown in FIG. 1, can be found in comparison of the performance of 0.338 Lapua Magnum vs. that of 0.338 Norma Magnum rifle cartridges. It is generally thought that the 0.338 Norma Magnum, which has a more obtuse shoulder angle and less overall internal volume, is a higher accuracy round as compared to the 0.338 Lapua Magnum.

The mechanism responsible for the increased accuracy of an alternative (in this case sharper) neck angle is thought to involve its effect of the convergence point for particles/gases during ignition. At some optimal angle, evenly applied pressure behind the bullet will result in the elimination of yaw prior to the projectiles entry into the rifling. In this example, sharper angles seemingly stabilize the projectile at this stage and result in a more accurate round.

Manufacturing a brass cartridge is currently performed by either extrusion or deep drawing of the brass into a tubular pre-form followed by die-forming or machining the final features (primer pocket, extractor groove, etc.). The manufacturing process for brass cartridges results in the internal and external surfaces of the case in the shoulder angle region remaining substantially parallel, as shown schematically in FIG. 2. This limits the degrees available to engineer optimal neck angles into ammunition formed from brass cartridges.

In contrast to the production process for brass cartridges, polymeric cartridges can be produced by injection molding. In this process, molten plastic is injected between an outer surface (mold) and an inner surface (core) to produce the desired geometries on both sides. This production process offers the distinct advantage of independent internal and external geometries in the neck angle region. Thus the internal shoulder angle of an injection molded case can be adjusted by changing the core against which it is molded, and this change does not affect the external angle that is controlled by the mold cavity. Accordingly, in many embodiments ammunition articles are provided where at least the neck region of the article casing is formed from a polymeric material, thus allowing for the engineering of such articles.

For the purposes of the present invention, the term “ammunition article” as used herein refers to a complete, assembled round of ammunition that is ready to be loaded into a firearm and fired. An ammunition article may be a live round fitted with a projectile, or a blank round with no projectile. An ammunition article may be any caliber of pistol or rifle ammunition and may also be other types such as non-lethal rounds, rounds containing rubber bullets, rounds containing multiple projectiles (shot), and rounds containing projectiles other than bullets such as fluid-filled canisters and capsules. The cartridge casing is the portion of an ammunition article that remains intact after firing. A cartridge casing may be one-piece or it may consist of two components or even higher number of components.

Hybrid polymer-metal cartridge casings are well known in the art and can be used in one embodiment of the present invention. In this embodiment, a polymeric caselet constitutes the forward portion of a cartridge casing, and a metallic cap forms the closed, rearward casing portion. The proportion of plastic to metal can vary, a larger percentage of plastic being preferred to maximize weight reduction, corrosion resistance, and other advantages of plastics. The amount of metal present is determined by the smallest metal cap size necessary to prevent cartridge failure during firing. Non-limiting amounts of polymeric material in a cartridge casing by weight are about 10%, more preferably about 20%, even more preferably about 30%, still more preferably about 40%, yet more preferably about 50%, even more preferably about 60%, more preferably about 70% and up.

Accordingly, in many embodiments an ammunition casing is a portion of the ammunition article that physically holds propellant, primer and projectile (if present). Thus, the ammunition casing is the portion of an ammunition article that remains after firing and is extracted out of the weapon.

Embodiments of Ammunition Casing

Turning to FIGS. 3a and 3b , there is shown an exemplary embodiment of an ammunition article (1) provided in accordance with embodiments of the present invention. The ammunition article includes an ammunition casing (2). The ammunition casing (2) may be comprised of a pressure vessel component (3) and lightweight component (4). Lightweight cap component (4) reduces the overall weight of the ammunition article without being in direct contact with propellant and thus allowing a wide variety of previously unsuitable lightweight materials to be used. Components (3) and (4) may be joined at the surfaces (3 a and 4 a), respectively, most preferably by a slip or interference fit, with or without augmenting the fit with adhesive or a retaining compound. Other methods that result in acceptable holding force are also acceptable, such as threads or overmolding in case of polymeric light-weight component.

A further embodiment of the present invention is illustrated in FIG. 3c , which shows an ammunition casing which comprises the first pressure vessel component being comprised of two sub-components, (5) and (6), with light-weight component (7) comprising the head or cap of the ammunition casing.

A further embodiment of the present invention is illustrated in FIG. 3d , which shows the pressure vessel component comprising of three individual components (8, 9 and 10) with lightweight component (11) at the head of the casing. Components (8 and 9) are typically polymeric in nature, while (10) is typically of metallic construction.

A further embodiment of the present invention is illustrated in FIG. 4 which shows the pressure vessel component (12) skeletonized and lightweight component (13) over-molded over it. In this embodiment, the pressure vessel skeleton also provided a degree of structural support for the extractor flange, while the lightweight component still comprises the exterior surface of the extractor.

According to the present invention, pressure vessel component may be comprised out of any suitable material. The preferred material for the one component pressure vessel is steel, although brass, aluminum and polymeric components could also be used. The preferred materials for the light weighting component are aluminum or fiber-filled polymers although other materials such as cermets, ceramics or non-fiber reinforced polymers are also acceptable. This approach is valuable as it maximizes the weight savings while at the same time not exposing any portion of the lightweight component to the combusting propellant gases.

In a preferred embodiment, a steel pressure vessel forms the forward portion of the ammunition casing, while portion of the ammunition casing head is formed from aluminum or an injection molded fiber-filled polymer. The steel pressure vessel houses a live primer. A propellant charge is introduced into the interior cavity formed by the pressure vessel. A projectile is inserted into the open end of the pressure vessel and secured with appropriate means. The light-weight component, most preferably aluminum or fiber-filled polymer, is attached to the pressure vessel component in such a manner as to not contact any of the propellant charge. The assembled ammunition article is loaded into a firearm chamber and fired. This approach is valuable as it maximizes the weight savings while at the same time not exposing any portion of the lightweight component to the combusting propellant gases, allowing the use of aluminum for example.

The external dimensions of the assembled casing are largely guided by the weapon chamber dimensions. The internal dimensions can vary according to application needs and fabrication methods. For example, owing to the greater steel strength, the wall thickness of the pressure vessel component may be reduced for additional weight savings.

The proportion of steel to aluminum can vary, a larger percentage of aluminum being preferred to maximize weight reduction. The amount of steel present is determined by the smallest pressure vessel size necessary to prevent cartridge failure during firing. Non-limiting amounts of light-weight material in a cartridge casing by weight are about 5%, more preferably about 10%, even more preferably about 20%, more preferably about 30% and up.

In another embodiment of the invention, the pressure vessel component is provided having a multi-piece design. In some such embodiments, as shown in FIG. 3c , the pressure vessel is comprised of a metallic portion (6) joined to a polymeric caselet portion (5), with the caselet comprising a polymeric material. The metallic portion of the pressure vessel houses a live primer and is joined securely to the caselet. A propellant charge is introduced into the interior cavity formed by the assembled casing. A projectile is inserted into the open caselet end and secured with appropriate means. The lightweight component, most preferably aluminum or fiber-filled polymer, is attached to the pressure vessel component in such a manner as to not contact any of the propellant charge. The assembled ammunition article is loaded into a firearm chamber and fired. This approach is valuable as it maximizes the weight savings while at the same time not exposing any portion of the lightweight component to the combusting propellant gases.

In another embodiment of the invention, the pressure vessel component is provided having a three-piece design (as shown in FIG. 3d ). The pressure vessel is comprised of a metallic portion (10) joined to a polymeric caselet portion, with the caselet comprising two components (8 & 9) fabricated out of polymeric materials. Two polymeric components can be fabricated out of same or different polymeric materials. The remainder of the ammunition article is assembled as per earlier embodiments.

Possible methods for securing projectile into the pressure vessel include, but are not limited to, mechanical interlocking methods such as mechanical crimping, ribs and threads, adhesives, molding in place, heat crimping, ultra-sonic welding, friction welding etc. Additional compounds may be introduced to facilitate waterproofness, for example asphalt, gasketing or cyanoacrylate compounds. These and other suitable methods for securing are also useful for securing individual pieces of a two-piece or multi-piece pressure vessel design to each other in the practice of the present invention.

Possible methods for securing lightweight component to the pressure vessel component include but are not limited to, mechanical interlocking methods such as slip fit, press fit, interference fit, mechanical crimping, ribs and threads, adhesives, molding in place, heat crimping, ultra-sonic welding, friction welding etc. The primary attachment method may be augmented by a secondary method such as threadlocker, retaining compound, adhesive, post-assembly crimp etc.

Many different types of ammunition articles are provided by the present invention. For example, embodiments of this invention may be used to produce ammunition components for various calibers of firearms. Non limiting examples include 0.22, 0.22-250, 0.221, 0.223, 0.243, 0.25-06, 0.270, 0.300, 0.30-30, 0.30-40, 30.06, 0.303, 0.308, 0.357, 0.38, 0.40, 0.44, 0.45, 0.45-70, 0.50 BMG, 500 Nitro, 5.45 mm, 5.56 mm, 6.5 mm, 6.8 mm, 7 mm, 7.62 mm, 8 mm, 9 mm, 10 mm, 12.7 mm, 14.5 mm, 20 mm, 25 mm, 30 mm, 40 mm and other non-standard (“wildcat”) calibers.

Testing ammunition produced using the materials of the present invention are done by firing fully assembled live ammunition articles. The pressure vessel component (single or multi-piece) is joined to the lightweight component (single or multi-piece). The resulting cartridges are loaded with a propellant charge, the type and amount of which can be readily determined by a skilled artisan and for which numerous references exist (for example Speer Reloading Manual, 7^(th) Printing 2005). A projectile is inserted into the open end of the cartridge and secured. The article is thus prepared for test firing. Any size, caliber, or type of ammunition article can be assembled for live testing.

Test firing ammunition provided by this invention can be performed using any type of firearm corresponding to the size or caliber of the article produced. Ammunition articles can be test fired from a single shot firearm, a semi-automatic firearm, or an automatic firearm. Ammunition may be fired individually or from a clip, magazine, or belt containing multiple ammunition articles. Articles may be fired intermittently or in rapid succession; the rate of fire is limited only by the capabilities of the firearm. Any number of standard brass ammunition articles may be fired in order to pre-heat the firearm chamber for testing under simulated sustained rapid-fire conditions.

Ammunition Casing Neck Engineering

The injection molding process used to produce the above described polymeric caselet designs offers considerable freedom in the design of the internal geometry of the part. Using this process, the possibilities for internal neck geometry are virtually limitless and highly independent of the external case geometry in this region. The present invention provides embodiments of internal geometries that will improve the accuracy of the round. In the following discussion, geometry will be discussed using the longitudinal axis as the “y” and the axis perpendicular to the longitudinal axis as “x”.

Several general cases are presented as examples of the geometric features covered by many embodiments.

Configuration 1—The internal geometry in the neck region is linear but non parallel with external neck line resulting in a ratio of angles that will be defined as the “internal to external wall angle ratio” or “IEWAR”. The endpoints that define the interior caselet geometry are also variable along the longitudinal axis of the ammunition article.

Configuration 2—The interior geometry in the neck region of the caselet is a circular arc with a designed, fixed radius that is blended into the straight neck region and the straight body region. The arc can have a focus on any point in the x-y plane allowing the final arc to be concave or convex relative to a consistent point of reference. As with Case 1, the start and end points of the arc are variable along the longitudinal axis of the ammunition article.

Configuration 3—The interior geometry of the ellipse having a major axis and minor axis with its position defined by a center point and two foci that lie on any point in the x-y plane. The elliptical arc is blended into the straight interior body and neck regions on either side.

Configuration 4—Multiple geometric features in series can be used to describe a more complicated internal geometry such as 2 or more arcs in series, 2 or more lines with varying angles relative to the x or y axis in series, or combinations of lines and arcs in series. In this case all start and end points of the features can have variable positions in the x-y plane.

Configuration 5—The internal caselet neck geometry can protrude into the caselet interior from the neck region in any specific two dimensional profile resulting in features that lie under the inserted projectile on the y-axis. These designs will result in a circular constriction of the internal caselet opening that is defined by a minimum radius having a position defined on the y-axis.

Configuration 1

In the general description above this configuration defines a ratio of angles that is a non-unity value. The external wall angle for a given caliber of ammunition is a fixed value determined by the chamber dimensions. This invention introduces the concept of a variable interior angle that is independent of the external angle and defined by start and end points on the y-axis as well as an angle relative to the same axis. After defining the caselet's interior neck geometry in the previously mentioned way, it is possible to describe this case for any ammunition article by the IEWAR quantity.

From FIGS. 5a and 5b , it can be seen that the internal geometry in this case can be completely described by the y-axis coordinates of the angle line's start and end points and the IEWAR for the given design. In the figures, 45° is the internal angle of the caselet making the IEWAR:

-   -   IEWAR External Angle/Internal Angle=15°/45°=0 333

Although the above example has a specific IEWAR of 0.333 the present invention covers IEWAR's intentionally designed to any non-unity value for internal geometry located on any position on the previously defined y-axis. Also transition regions that blend the internal angle into the straight sections of the neck and body may be present in the form of chamfers or fillets. In many embodiments, the IEWAR ratios are smaller than 0.95, in some embodiments less than 0.90, in still other embodiments less than 0.75, and in still other embodiments less than 0.50 and so on.

In certain calibers, it may be possible to construct IEWAR ratios that maximize the inherent accuracy of the round by increasing the IEWAR ratios. In that case, the IEWAR would be larger than unity, in some embodiments larger than 1.10; and in still other embodiments larger than 1.20 and even larger.

Configuration 2

An additional geometry covered by embodiments is that of a continuous constant radius arc blended into the straight wall sections of the caselet body and neck. The arc can have a focus at any point on the x-y plane and have start/stop points at any position along they-axis. The position of the arc's focus will determine whether the section is convex as dictated by the specifications of the chamber of intended use are decoupled from the interior geometry and therefore remain unchanged.

FIGS. 6a and 6b illustrate both convex and concave internal neck geometry characteristic of a “configuration 2” in accordance with embodiments. The dimensions in the drawings are not specified as the radius arc and position along they-axis are variable.

Using the above definitions it is possible to derive a useful descriptive quantity as the ratio of arc radius to vertical distance that it covers in the interior neck region. This quantity will be named “Radius to Internal Neck Length Ratio” (RINLR). As an illustration, the radius of the internal arcs depicted in FIGS. 6 and 7 will be assigned a value of 0.990 inches. The vertical distance covered (between the two horizontal dotted lines) can be assigned a value of 0.326 inches. In this specific case, calculating the RINLR for the case would proceed as follows:

-   -   RINLR Internal Neck Arc Radius/Internal Neck         Length=0.990/0.326=3.04

Embodiments cover internal neck geometries described by a single circular arc starting and finishing along two points on they-axis and having RINLR values between 0.1 and 50, more preferred between 0.5 and 25, even more preferred between 0.75 and 20.

Configuration 3

In embodiments described by “Configuration 2”, as depicted in FIGS. 6a and 6b , the arc describing the internal neck geometry is a circular arc. In embodiments of another configuration related to Configuration 2, the arc of the internal neck geometry is elliptical. In this case, a single arc can still be used to describe the internal neck geometry however its complete definition will include coordinates for two foci as well as y-coordinates for at the arc's terminuses. In this configuration, the position of the two foci on the x-y plane will determine the level of concavity or convexity of the internal neck wall, as shown schematically in FIG. 7.

Using the mathematical definition of an ellipse, a useful descriptive quantities of the said embodiments can be derived. An ellipse is defined as: a curved line forming a closed loop, where the sum of the distances from two points (foci) to every point on the line is constant. This concept is illustrated in FIG. 8. The above definition of an ellipse allows this configuration of the said invention to be defined as an internal case neck with terminuses at any two points on the y-axis (longitudinal axis of the case) shaped as an elliptical arc belonging to an ellipse that has foci at any point on the x,y plane and values of a+b (from FIG. 8) equaling any real number in the range of 0 to 10 inches.

Configuration 4

Any of the previously described embodiments can be combined in series to form a significantly more complex geometry. Examples include but are not limited to multiple lines in series with no consecutive lines being co-linear, multiple arcs in series such as defined by a spline curve, and a combination of straight lines at various angles and arcs both circular and elliptical in series. These features in series can also contain transition of blend regions that link the lines with chamfers and fillets.

Configuration 5

Embodiments of the current invention also allows the creation of protruding features in the hollow body region of the ammunition article. One example of such an embodiment is illustrated in FIG. 9. It will be understood that embodiments of the current invention are not limited to any single geometry of the protrusion. It is defined by the criteria that the body of the article at any point on they-axis breaks a vertical plane that projects toward the ammunition article base from the point on the projectile in which its maximum radius occurs. Two instances of this plane (if projecting the coordinate system shown below into 3 dimensions the plane would be the YZ plane) are shown in FIG. 9 as dotted lines extending vertically in the −y direction from the max OD of the projectile on either side. The protrusion can be continuous around the inner circumference of the ammunition article, intermittent as recurring features or a single instance on a given vertical plane. Although FIG. 9 below shows the feature impinging upon the projectile, this is not a requirement. The same accuracy benefits may be incurred by protruding features that are not located high enough on the y-axis to result in contact with the projectile.

EXEMPLARY EMBODIMENTS Example 1 Test Firing for Configuration 1

Four groups of rounds are prepared prior to range firing. The first group is standard Winchester 0.308 caliber brass ammunition. Groups 2, 3, and 4 are polymeric ammunition with external geometry mimicking standard 0.308 caliber rounds. The internal geometries of groups 2, 3 and 4 differ only in IEWAR values (configuration 1 of the said invention). Group 2 has an IEWAR of 0.90. Group 3 has an IEWAR of 0.75. Group 4 has an IEWAR of 0.50. All rounds are loaded to target ballistic specifications of 2850 fps and 60,000 psi using a 155 grain projectile.

A Mossberg® 100ATR 0.308 Winchester Bolt-Action Rifle with Scope is used to bench fire 10 rounds of standard Winchester 0.308 caliber brass ammunition at a distance of 100 yards. The standard brass ammunition as stated in the previous sections has an internal neck angle essentially parallel with the external neck angle therefore making the IEWAR for the case equal to 1 (unity). Standard “minute of angle” calculations give a value for the group of 10 rounds to be 0.92 MOA. Subsequently, 10 rounds of each of the remaining 3 groups are bench fired in the same rifle. MOA calculations for Groups 2, 3, and 4 result in values of 0.76, 0.65, and 0.48 respectively. These results show the relationship between IEWAR and MOA values. As IEWAR moves further from unity, MOA improves.

Example 2 Test Firing for Configuration 2

Four groups of rounds are prepared prior to range firing. The first group is standard Winchester 0.308 caliber brass ammunition. Groups 2, 3, and 4 are polymeric ammunition with external geometry mimicking standard 0.308 caliber rounds. The internal geometries of groups 2, 3 and 4 are examples of “configuration 2” of the said invention and differ RINLR of 3. Group 4 has a RINLR of 0.5. All rounds are loaded to target ballistic specifications of 2850 fps and 60,000 psi using a 155 grain projectile.

A Mossberg® 100ATR 0.308 Winchester Bolt-Action Rifle with Scope is used to bench fire 10 rounds of standard Winchester 0.308 caliber brass ammunition at a distance of 100 yards. The standard brass ammunition as stated in the previous sections has an internal neck angle essentially parallel with the external neck angle therefore making RINLR impossible to calculate. Standard “minute of angle” calculations give a value for the group of 10 rounds to be 0.92 MOA. Subsequently, 10 rounds of each of the remaining 3 groups are bench fired in the same rifle. MOA calculations for Groups 2, 3, and 4 result in values of 0.65, 0.68, and 0.80 respectively. These results show the accuracy improvement realized by implementation of the said invention in the “configuration 2” incarnation. Also as the RINLR values for the polymeric rounds move into the more desirable range, accuracy improves (Groups 2 and 3 are in the more favorable RINLR value range relative to group 4.

Example 3 Test Firing for Configuration 3

Two 10 round groups of are prepared prior to range firing. The first group is standard brass .50 BMG. The second group consists of polymeric ammunition with a shape that can be called a simple example of “configuration 4” of the said invention. The internal geometry of group two is created by molding two features in series in the shoulder region. Immediately below the neck of the case, the internal shoulder can be described as linear but non-parallel with the external shoulder (similar to configuration 1). The internal wall has an angle of 20° from vertical while the external wall has an angle of 15.73 from vertical. Using these values, the IEWAR for this segment is calculated to be 0.79. In this example however, the non-parallel line does not extend for the full length of the internal neck region. At a vertical distance of 0.092″ from the neck/shoulder interface, the linear internal geometry is joined to a circular arc of radius 0.224″. The circular arc extends for a vertical distance of 0.076″. This makes the total vertical length of the internal neck (linear and arc regions) 0.168″. Dividing the arc radius by the total internal neck length gives the RINLR to be 1.33. This geometry is shown schematically in FIG. 10.

Groups one and two are both loaded characteristic of rounds targeting a velocity of 2850 fps while producing chamber pressures of 60,000 psi. Both groups are bench fired at 200 yards using a Barrett M82A1 rifle system. Standard minute of angle calculations reveal the MOA for the standard brass to be 0.85. The MOA for the polymeric ammunition is calculated to be 0.76. A diagram of the polymeric rounds internal geometry can be found below.

Having described several embodiments, it will be recognized by those skilled in the art that various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the disclosure. Additionally, a number of well-known processes and elements have not been described in order to avoid unnecessarily obscuring the present disclosure. Accordingly, the above description should not be taken as limiting the scope of the disclosure.

Those skilled in the art will appreciate that the presently disclosed embodiments teach by way of example and not by limitation. Therefore, the matter contained in the above description or shown in the accompanying drawings should be interpreted as illustrative and not in a limiting sense. The following claims are intended to cover all generic and specific features described herein, as well as all statements of the scope of the present method and system, which, as a matter of language, might be said to fall therebetween. 

What is claimed is:
 1. An ammunition article comprising; a casing defining a generally cylindrical hollow body having internal and external walls, the casing having a cap at a first end thereof and a pressure vessel at a second end thereof, the pressure vessel having a proximal end defining a body region and a distal end defining a neck region, wherein the cap is interconnected with the proximal end of said pressure vessel such that the casing at least partially encloses an internal volume, and wherein the diameter of the pressure vessel narrows from a first diameter at the body region to a second diameter at the neck region; wherein at least the neck region of the pressure vessel at least partially comprises a substantially polymeric material; wherein the geometry of the internal and external walls of the casing in the neck region of the casing are independent of each other; and wherein the casing in the neck region defines an internal wall that forms a curved arc relative to a linear external wall.
 2. The ammunition article according to claim 1, wherein the curved arc is one of either a convex or concave circular arc.
 3. The ammunition article according to claim 2, wherein the arc of the internal wall of the neck region defines a ratio of the radius of the arc to the length of the neck region of the casing of between about 0.1 and
 50. 4. The ammunition article according to claim 2, wherein the arc of the internal wall of the neck region defines a ratio of the radius of the arc to the length of the neck region of the casing of between about 0.5 and
 25. 5. The ammunition article according to claim 2, wherein the arc of the internal wall of the neck region defines a ratio of the radius of the arc to the length of the neck region of the casing of between about 0.75 and
 20. 6. The ammunition article according to claim 1, wherein the curved arc forms a generally elliptical arc relative to a linear external wall.
 7. The ammunition article according to claim 6, wherein the elliptical arc of the internal wall of the neck region is defined by an ellipse value determined by the sum of the distances from any two points within a plane of the ellipse to any single point on the circumference of the ellipse, and wherein the ellipse value ranges from about 0 to 10 inches.
 8. The ammunition article according to claim 1, wherein the internal wall of the neck region is defined by a plurality of regions selected from the group of non-colinear consecutive lines, more than one arc in a spline curve, a combination of non-parallel lines, and a combination thereof.
 9. The ammunition article according to claim 8, wherein the plurality of regions are blended together using chamfers or fillets.
 10. The ammunition article according to claim 1, wherein the interior wall of the neck region of the casing has at least one point that is narrower than the inner diameter of the distal end of the pressure vessel in which a projectile would be inserted.
 11. The ammunition article according to claim 10, wherein the at least one point in the neck region is disposed such that a projectile inserted into the casing would impinge thereon.
 12. The ammunition article according to claim 1, wherein the casing is one-piece.
 13. The ammunition article according to claim 1, wherein the polymeric material comprises at least 10% of the casing by weight.
 14. The ammunition article according to claim 1, wherein the cap comprises a metal.
 15. The ammunition article according to claim 1, wherein the cap and the caselet are joined using an interconnection selected from the group consisting of a snap fit, threads, snap fit in conjunction with an adhesive, and threads in conjunction with an adhesive.
 16. The ammunition article according to claim 1, wherein the casing is closed at its distal end and contains no projectile.
 17. The ammunition article according to claim 1 additionally comprising a projectile fitted into the distal end of the casing.
 18. The ammunition article according to claim 17 wherein the projectile is secured to the casing by an interconnection selected from the group consisting of molding the polymeric material around the projectile, mechanical interference, an adhesive, ultrasonic welding, the combination of molding in place and adhesive, and hot crimping after molding.
 19. The ammunition article according to claim 1, wherein the pressure vessel comprises at least two pieces. 